`star` Axial Skeleton
`star` Skull
`star` Vertebral Column
`star` Ribcage


● `color{brown}("Skeletal system")` consists of a framework of `color{brown}("bones")` and a `color{brown}("few cartilages.")`

● This system has a `color{violet}("significant role")` in movement shown by the `color{violet}("body.")`

● `color{violet}("Bone")` and `color{violet}("cartilage")` are `color{brown}("specialised connective tissues.")`

● The former has a very hard matrix due to `color{brown}("calcium salts")` in it and the latter has `color{violet}("slightly pliable matrix")` due to `color{brown}("chondroitin salts.")`

● In human beings, this system is made up of `color{brown}("206 bones")` and a `color{violet}("few cartilages.")`

● It is grouped into two principal divisions – the `color{brown}("axial")` and the `color{brown}("appendicular skeleton.")`

● `color{brown}("Axial skeleton")` comprises `color{brown}("80 bones")` distributed along the main `color{violet}("axis")` of the body.

● The `color{brown}("skull, vertebral column, sternum")` and `color{brown}("ribs")` constitute `color{violet}("axial skeleton.")`


● The `color{brown}("skull")` is composed of two sets of `color{violet}("bones")` – `color{brown}("cranial and facial,")` that totals to `color{violet}("22 bones.")`

`star` `color{green}("Cranial Bones:")`

● `color{violet}("Cranial bones")` are `color{brown}("8")` in number.

● They form the `color{violet}("hard protective")` outer covering, `color{brown}("cranium")` for the `color{violet}("brain.")`

`star` `color{green}("Facial Bones:")`

● The `color{violet}("facial region")` is made up of `color{brown}("14 skeletal elements")` which form the front part of the `color{violet}("skull.")`

● A `color{violet}("single U-shaped bone")` called `color{brown}("hyoid")` is present at the base of the `color{violet}("buccal cavity")` and it is also included in the `color{violet}("skull.")`

● Each middle ear contains three `color{violet}("tiny bones")` – `color{brown}("Malleus, Incus and Stapes")`, collectively called `color{brown}("Ear Ossicles.")`

● The `color{violet}("skull region articulates")` with the superior region of vertebral column with the help of `color{brown}("two occipital condyles (dicondylic skull).")`


● Our `color{brown}("vertebral column")` is formed by `color{brown}("26 serially arranged")` units called `color{violet}("vertebrae")` and is `color{violet}("dorsally placed.")`

● It extends from the base of the `color{violet}("skull and constitutes")` the main framework of the `color{violet}("trunk.")`

● Each vertebra has a `color{violet}("central hollow portion")` ( `color{brown}("neural canal")`) through which the `color{violet}("spinal cord passes.")`

● First vertebra is the `color{brown}("atlas")` and it articulates with the `color{violet}("occipital condyles.")`

● The `color{violet}("vertebral column")` is differentiated into `color{brown}("cervical (7), thoracic (12),")` `color{violet}("lumbar (5), sacral (1-fused)")` and `color{brown}("coccygeal (1-fused)")` regions starting from the `color{violet}("skull.")`

● The number of `color{violet}("cervical vertebrae")` are seven in almost `color{brown}("all mammals")` including human beings.

● The `color{violet}("vertebral column protects")` the `color{violet}("spinal cord,")` supports the head and serves as the point of attachment for the ribs and `color{violet}("musculature of the back. ")`


● `color{brown}("Sternum")` is a `color{violet}("flat bone")` on the ventral midline of `color{violet}("thorax.")`

● There are `color{brown}("12 pairs")` of `color{brown}("ribs.")`

● Each rib is a `color{violet}("thin flat bone")` connected dorsally to the `color{violet}("vertebral column")` and ventrally to the sternum.

● It has two articulation surfaces on its `color{violet}("dorsal end")` and is hence called `color{brown}("bicephalic.")`

`star` `color{green}("True Ribs ")`

● First seven pairs of `color{violet}("ribs")` are called `color{brown}("true ribs.")`

● `color{violet}("Dorsally,")` they are attached to the `color{violet}("thoracic vertebrae")` and ventrally connected to the sternum with the help of `color{violet}("hyaline cartilage.")`

`star` `color{green}("Vertebrochondral (false) ribs:")`

● The `color{violet}(" 8th, 9th and 10th pairs")` of `color{violet}("ribs")` do not articulate directly with the sternum but join the `color{violet}("seventh rib")` with the help of `color{violet}("hyaline cartilage.")`

● These are called `color{brown}("vertebrochondral (false) ribs.")`

`star` `color{green}("Floating Ribs:")`

● Last `color{violet}("2 pairs (11th and 12th)")` of ribs are not connected `color{violet}("ventrally")` and are therefore, called `color{brown}("floating ribs.")`

`star` `color{green}("Rib cage:")`

`color{violet}("Thoracic vertebrae, ribs")` and `color{violet}("sternum")` together form the `color{brown}("rib cage.")`